C. Accept EFTA/EEA largely as is, at least on the main principles. Of course details will be negotiated, but rules, incl FoM will stand;

D. Attempt to withdraw Art50. Will probably still just about get away with it, with agreement to drop a few current UK perks in next MFF.

A is obviously absurdly catastrophic. B will, as Ivan Rogers rightly noted, take at least 5-7 yrs of uncertainty with no guaranteed outcome or end. C is reasonable, and would reduce harm compared to A & B, but requires UK accepting ‘Laws by Fax’ with little or no say in them.

Which, of course, leaves us with D…

I should also add a note on ‘reforming’ SM or Freedom of movement, which seems to be Labour policy. Why would the EU27 possibly be interested in changing a cornerstone of the Treaties, a fundamental principle, just because it’s UK’s preference? Particularly when it is in the UK’s power simply to ask to remain in the SM and accept the conditions of it like Norway and others do? Opening this would obviously lead to calls from EFTA/EEA members for the same deal for them. Switzerland tried this, and had to concede.

UK will not dictate terms, the EU27 will. The EU27’s concession is that, despite the damage already caused by UK, SM is still on the table.